The reason why I don't think it's a prototype is because of the sailess submarine they had earlier. The sailess sub is pretty much the same size, also single hulled, which is most likely a prototype/experimental platform. Why build two experimental sub of the same size, only 2 years apart. I see PLAN want something for the shallow waters within the first island chain. This can liberate the larger convential subs to patrol areas around the second island chain and indian ocean and gaining experience for the eventual long range patrol of the nuclear subs. China still have some Mings that want to replace. The yellow and east china sea only have a depth of 80 meters and not suitable for large submarine operation. The small sub is also useful to delivery frogman for special operations.